Is solar a good backup for when the power goes out?

Not typically, but it can be. Solar systems need somewhere to send the energy they produce, or it doesn’t work. The vast majority of solar users are connected to the grid. When your panels are making more energy than you’re using, the excess goes back out into the wide world, making your meter run backward in the process.
You can, however, implement a battery backup system along with your solar array. Not only does this give you a little extra juice when the sun goes down, but it also provides some extra brains that allow your system to work independently of the grid. On the hot, sunny days following a hurricane, the proper system could have you running your AC, your fridge, and your television with gusto, while your neighbors sweated it out to books and beanie weenies in a can!